Not applicable.
Not applicable.
The present invention relates to a process and an apparatus for improving the surface properties of polymers, such as improving adhesion or improving wicking, i.e., conveying liquid by capillary action.
Existing technologies for surface treating polymers include abrasive buffing, etching, solvent washing, chlorinated polyolefin (CPO) treatment, exposure to corona or glow discharge treatments, and plasma or flame treatments. Fluorination and oxyfluorination technologies also exist. Each of these technologies has its own shortcomings.
Subjecting a polymer surface to abrasive buffing and etching (solvent or otherwise) makes it difficult to obtain a smooth and lustrous paint coating on the polymer surface thereafter. Solvent washing and CPO treatments generate large volumes of waste by-products and use solvents which contribute to volatile organic compound emissions if not captured and destroyed. Corona and glow discharge treatments tend to age and become ineffective with time. Plasma and flame treatments do not provide a homogeneous surface modification on a convoluted part.
The disadvantages of present fluorination and oxyfluorination processes having surface modification as an objective are manifest. Some of these processes need substantial apparatus because they entail moving the fluorine gas from a holding chamber to a reaction chamber and back again. Substantial apparatus may also be required because these processes use very high concentrations of fluorine or relatively long treatment cycles during which pressure is increased gradually. As more apparatus is required, costs increase. Processes utilizing fluorine pose a threat to safety because fluorine is a highly toxic, highly corrosive, irritating gas. Any process that uses relatively high temperatures, pressure, concentrations and/or volumes of fluorine is hazardous due to an increased possibility of fire or leakage. Finally, these processes raise the pollution factor because of the amount of fluorine and/or fluorine by-products, such as hydrogen fluoride, which must be disposed of after the completion of the fluorination process.
Numerous attempts have been made to improve the surface properties of polymers. For example, U.S. Pat. No. 5,654,378 (Dehennau et al) discloses articles including polyolefins which are surface treated and printed with inks, such as PVC inks. The article surface includes fluorine and oxygen in concentrations such that the oxygen/carbon atom ratio at a depth of 1.5 nm is at least 0.08 and the fluorine/carbon atom ratio is at least 90% but not more than 290% of the oxygen/carbon atom ratio.
U.S. Pat. No. 5,654,378 also relates to a process for the manufacture of such articles that involves an oxidation stage and a fluorination stage. By example, the patent shows that an ambient temperature, sub-ambient pressure fluorination or fluoroxidation process which exposes a polymer to approximately 20 millibars of F2 for approximately seven minutes by gradually raising the gas pressure over approximately 5 minutes from 200 millibars to 400 millibars at a rate of 40 millibars per minute for a total fluorine exposure time of approximately fifteen minutes can provide an ink-receptive surface, particularly when the oxygen content on the surface is high.
European Patent Application Publication No. 0-502-303-A1 teaches a process for the treatment of objects with a gas containing fluorine as well as an arrangement for carrying out the process. In particular, the publication teaches the design of fluorination equipment that is arranged to be operated always in a sub-ambient pressure mode with fluorine being recycled. It is silent on the rate of pressurization.
U.S. Pat. No. 4,752,428 (Williams et al) teaches a process for making shaped articles by injecting a thermoplastic or thermoset polymer into a mold cavity in which a concentration of fluorine and oxygen is contained at atmospheric pressure while the polymer is being injected into the mold. The process results in shaped articles having altered physical and chemical characteristics, including improved surface adhesion.
U.S. Pat. No. 4,764,405 (Bauman et al) discloses a method for improving the barrier properties of thermoplastic substrates. A surface of the thermoplastic substrate is contacted with a reactive gas stream having a particular concentration of fluorine and oxygen.
U.S. Pat. No. 4,743,419 (Bierschenk) teaches an on-line film fluorination apparatus cooperative with a continuous polymer film extruding apparatus. In one embodiment, a continuous feed film is introduced into a closed cabinet having guide rollers for directing the film into a housing. The film passes around a roller formed of sintered nickel to enable gaseous impregnation of a surface of the film with a gas flow including fluorine. The gas acts on the exposed face of the film, changing the surface of the polymer film, thereby providing a relatively thick surface upgrading of the film. After exposure to the fluorine, the film passes a closed vacuum container having an open face for drawing off unreacted fluorine for recapture and recycling. The film emerges from the closed cabinet having a modified surface and the cabinet is evacuated with a slight negative pressure.
U.S. Pat. No. 4,484,954 (Tarancon) teaches a process for the halogenation of solid polymeric or metallic material. A halogen is introduced into an evacuated chamber and is recirculated.
U.S. Pat. No. 4,404,256 (Anand et al) relates to low energy fluorinated polyolefin surfaces and to fluorinated polymers produced therewith. This patent teaches plasma fluorinations of surfaces to obtain lightly fluorinated oxygen-free surfaces of less than 200 Angstroms.
U.S. Pat. Nos. 4,296,151 and 4,237,156 (Boultinghouse) each teach treating the surface of a solid article made from a polymer, such as polyolefin or polystyrene, with a fluorine-containing gas to render the article receptive to adhesion.
U.S. Pat. No. 4,142,032 (D""Angelo) teaches a process for achieving significant improvements in the barrier properties of polymeric articles such as films and containers by surface treatment with both fluorine and bromine.
U.S. Pat. No. 4,081 574 (Hawkins et al) discloses an apparatus and process for exposure of articles to reactive gaseous fluids to alter their surface characteristics. The articles are exposed to one or more fluids which are transferred back and forth from a reaction chamber to a holding chamber. As the fluids are transferred, they pass through a trap designed to remove reaction by-products without affecting valuable reactant fluids.. Since the fluids can be transferred under vacuum and the overall reaction can take place at relatively low temperature, the process provides a convenient and safe method for handling reactive fluids. The process is particularly useful for the fluorination of a variety of articles such as plastic containers, aerosol bottles and films to improve their barrier resistance to solvents and gases.
U.S. Pat. No. 4,020,223 (Dixon et al) teaches surface modification of polyolefin and polyacrylonitrile fibers using elemental fluorine and low oxygen blends for improved oil release and moisture transport characteristics.
U.S. Pat. No. 4,009,304 (Dixon et al) teaches a process for improving adhesion of polyester yarn, tire cord or fabric and polyester reinforced rubber goods such as tires. Improved adhesion is achieved by fluorinating the polyester yarn, tire cord or fabric prior to incorporation into the tire or rubber goods.
U.S. Pat. No. 3,988,491 (Dixon et al) discloses a process for improving dye receptivity and soil and stain release properties of fiber-formed materials, such as polyesters and polyamides. The improved properties are achieved by subjecting the fibers to fluorine treatment in the presence of little or no oxygen for brief periods of time.
U.S. Pat. No. 3,413,266 (Saines et al) teaches fluorination of polycarbonate films using elemental fluorine at sub-ambient pressures.
U.S. Pat. No. 2,811,468 (Joffre) teaches post-treatment of polyethylene films and containers to improve gas barrier properties.
U.S. Pat. No. 2,715,075 (Wolinski) relates to a process for treating the surface of polyethylene structures, particularly polyethylene film, to promote the adhesion thereto of printed inks and various other materials.
U.S. Pat. No. 2,502,841 (Henderson) relates to polyethylene structures in which the surface which is to receive ink compressions has been modified so that the dried ink compressions will firmly and tenaciously adhere thereto. The patent also teaches a method for preparing such surfaces.
U.S. Pat. No. 4,830,810 (Ufer et al) teaches a method of blow molding and fluorinating plastic containers that is carried out in essentially three steps including blow molding of the container at a predetermined pressure in a mechanically locked mold with an inert gas, testing the meld for pressure tightness at a second higher level of pressure with an inert gas and thereafter introducing a fluorine containing gas into the mold at a third level of pressure.
U.S. Pat. No. 5,487,810 (Thurm et al) teaches use of sulphur hexafluoride plasma to improve the surface characteristics of plastic components for the adhesion of coatings especially metal coatings. Under this method, the plastic surfaces are kept free of fluorine deposits or inclusions during the pre-treatment.
U.S. Pat. No. 5,484,651 (Sasaki et al) teaches improving the hydrophilicity of polyolefin non-woven fabric webs by exposing them to fluorine and oxygen.
U.S. Pat. No. 5,744,257 (Carstens) teaches a process for producing a composite material comprising a cementitious substrate which is strengthened or reinforced with reinforcing material which adheres thereto. Adhesion of the substrate component to the reinforcing component is enhanced by subjecting the reinforcing component to surface fluorination prior to bringing the components into contact with each other.
While the aforementioned processes may be suitable for their intended purposes, it would be a significant advance in the art to provide a process for rendering the surface of a polymer adherent with other materials by exposing it to a fluorine gas, wherein the process could be performed in a relatively shorter cycle time, with a relatively lower concentration of fluorine and utilizing relatively less apparatus .
It is desired to have a process and an apparatus for improving the surface properties of polymers which reduce the amount of treatment gas utilized during the process.
It is further desired to have a process and an apparatus for improving the surface properties of polymers which reduce the cycle time for treatment during the process.
It is still further desired to have a process and an apparatus for improving the surface properties of polymers which overcome the disadvantages of the prior art.
It is still further desired to have a process and an apparatus for improving the surface properties of polymers which are simpler and more economical than the prior art.
It is still further desired to have a process and an apparatus for improving the surface properties of polymers which are more reliable in operation than the prior art.
It is still further desired to have a process and an apparatus for treating a polymer surface to render the surface receptive to other materials such as adhesives, glues, coatings, paints, inks, decorations, and the like.
It is still further desired to have a process and an apparatus for treating a polymer surface to render the surface receptive to adhesion with other dissimilar polymers.
It is still further desired to have a process and an apparatus for improving the surface properties of polymers in a reduced cycle time.
It is still further desired to have a process and an apparatus for improving the surface adhesion of polymers that require the use of lower concentrations of treatment. gas.
It is still further desired to have a process and an apparatus for improving the surface adhesion of polymers wherein toxic treatment gas can be evacuated more easily from the reaction vessel.
It is still further desired to have a process and an apparatus for improving the surface adhesion of polymers wherein toxic treatment gas can be disposed of more easily and economically.
It is still further desired to have a process and an apparatus for improving the surface adhesion of polymers that enable use of a smaller reaction vessel.
It is still further desired to have a process for improving the surface adhesion of polymers that utilizes less apparatus.
It also is desired to have a process and an apparatus for improving the surface adhesion of polymers that results in more uniform distribution of treatment gas throughout the reaction chamber.
The present invention discloses methods and an apparatus for modifying the surface chemistry of an article having at least one surface region that includes at least one polymer. The invention involves exposing the article to a treatment gas in a reaction chamber. Lower concentrations of treatment gas are required to achieve the same improved surface properties as achieved under the prior art. Also, shorter cycle times are required to achieve the same improved surface properties as achieved under the prior art. In addition, since lower concentrations of treatment gas are utilized, evacuation from the reaction chamber is easier, and lower quantities of waste are generated, making disposal less costly.
A first embodiment includes multiple steps. The first step is to place one or more articles in a closed reaction chamber, which is evacuated to a suitable negative pressure. After evacuation, a treatment gas is rapidly injected into the reaction chamber, the treatment gas having an essentially predetermined composition comprising one or more components which are reactive with the articles within the reaction chamber. The treatment gas is allowed to react with the articles within the closed reaction chamber. The treatment gas is then removed from within the reaction chamber and is replaced with an inert gas at about atmospheric pressure. Finally, the treated articles are removed from the reaction chamber. The method described herein may be utilized for improving the adhesion of the articles with other materials such as paint, adhesives or dissimilar polymers. Alternatively, the method may be utilized for improving the wicking ability of the articles.
The articles to be surface treated under this invention include at least one surface that is formed of a polymer that is amenable to surface modification by the treatment gas. The polymeric surface may be of a thermoplastic or a thermoset polymer. The polymeric material may be elastomeric in nature. The polymeric surface may be formed of a polymer or copolymer of olefins, styrenes, dienes, epoxies, vinyl or vinylidene chloride or fluoride, polycarbonates, polyesters, polyethers, polyacetals, polyacrylates, polymethacryates, polyamides, polyimides, polysulfones, polyphenylene ethers, polyaryletherketones and the like and blends thereof that are found amenable to surface modification.
In the first embodiment, the treatment gas is a mixture of fluorine and oxygen in an inert gas diluent. For example, the mixture may include from about 0.01% to about 1% fluorine and from about 0.01% to about 21% oxygen. Possible diluents include but are not limited to carbon dioxide, SF6, nitrogen, dry air, argon, and helium.
In the first embodiment, the treatment gas is stored in a storage vessel prior to being transferred into the reaction chamber. In one variation, the storage vessel may be of a fixed volume with the treatment gas stored therein being maintained at a pressure above atmosphere. Under this variation, the reaction chamber is maintained at a negative pressure. When the storage vessel is placed in communication with the reaction chamber, treatment gas is rapidly injected into the reaction chamber through pressure equalization. In another variation, the storage vessel may be of a construction that allows its volume to decrease, such as a piston-within-a-cylinder or a gas bladder type construction. Under this variation, treatment gas is rapidly injected into the reaction chamber by decreasing the volume of the storage vessel by movement of the piston within the cylinder or compression of the gas bladder rather than through pressure equalization.
In another variation of the first embodiment, the treatment gas is injected into the reaction chamber by sparging or spraying to ensure a good distribution of the treatment gas over the surface of the articles placed within the reaction chamber.
In another variation of the first embodiment, the treatment gas is held in static contact with the article.
In another variation of the first embodiment, the treatment gas is agitated within the reaction chamber to ensure a good distribution of the treatment gas over the surface of the articles placed within the reaction chamber.
In another variation of the first embodiment, the treatment gas is rapidly injected until the reaction chamber reaches an absolute pressure of approximately 900 millibars.
In another variation of the first embodiment, the reaction chamber is evacuated to an absolute pressure of no more than approximately 200 millibars and preferably no more than approximately 10 millibars prior to injection of the treatment gas into the reaction chamber.
In another variation of the first embodiment, the treatment gas is rapidly injected into the reaction chamber within a time period of about one second.
In another variation of the first embodiment, the treatment gas is rapidly injected into the reaction chamber at a rate sufficient to cause a temperature increase within the reaction chamber of at least five degrees Celsius (5xc2x0 C.).
In another variation of the first embodiment, the treatment gas is allowed to react with the articles placed within the reaction chamber for at least about 0.5 seconds and no more than ten seconds.
In another variation of the first embodiment, the step of removing the treatment gas from within the reaction chamber includes the sub-step of flowing a predetermined quantity of an inert gas through the reaction chamber after the reaction.
In another variation of the first embodiment, the step of removing the treatment gas from within the reaction chamber includes the sub-steps of creating a vacuum within the reaction chamber and thereafter flowing a predetermined quantity of an inert gas through the reaction chamber.
In another variation of the first embodiment, the step of rapidly injecting a treatment gas into the reaction chamber includes the sub-step of pressurizing the reaction chamber at a rate of pressurization of no less than 100 millibars per second, wherein a concentration of fluorine in the treatment gas is less than about 20%.
In another variation of the first embodiment, the step of rapidly injecting a treatment gas into the reaction chamber includes the sub-step of pressurizing the reaction chamber with the treatment gas at a pressurization rate of between approximately 500 millibars per second and approximately 8000 millibars per second. Under this variation, the treatment gas is injected into the reaction chamber in less than about two seconds and the concentration of fluorine in the treatment gas is approximately 100 ppm. The treatment gas is allowed to react with the articles within the closed reaction chamber for a time period of approximately five seconds.
In another variation of the first embodiment, the treatment gas is injected into the reaction chamber at a predetermined rate of pressurization of at least no less than approximately 50 millibars per second and preferably more than approximately 200 millibars per second and most preferably more than approximately 500 millibars per second.
In another variation of the first embodiment, the treatment gas is rapidly injected into the reaction chamber within a time period of about five seconds.
In another variation of the first embodiment, the treatment gas is rapidly injected into the reaction chamber within a time period of about ten seconds.
In yet another variation of the first embodiment, the treatment gas is removed from the reaction chamber by evacuation.
A second embodiment has one step in addition to the steps in the first embodiment. The additional step is to preheat the treatment gas to a selected temperature, e.g., in the range of about 30 to about 60 degrees Celsius (xc2x0C.), while the treatment gas is contained within the storage vessel. In a variation of this second embodiment, the treatment gas may be preheated once it has left the storage vessel as it is being rapidly injected into the reaction chamber.
A third embodiment has one step in addition to the steps in the first embodiment. The additional step is to monitor the pressure within the reaction chamber and within the storage vessel during the steps of evacuating the reaction chamber, injecting the treatment gas, and reacting the treatment gas with the articles placed within the reaction chamber.
A fourth embodiment has one step in addition to the steps of the first embodiment. The additional step is to introduce a neutralizing gas into the reaction chamber to lessen the toxicity of the treatment gas prior to removing the treatment gas from within the reaction chamber. In a variation of the fourth embodiment, the treatment gas includes a concentration of fluorine and the neutralizing gas includes a concentration of hydrogen. The neutralizing gas reacts with the treatment gas within the reaction chamber to form hydrogen fluoride.
The present invention also includes an apparatus for modifying the surface chemistry of an article, the article having at least one surface region including at least one polymer. The apparatus includes (1) a closed reaction chamber adapted to receive the article; (2) means for evacuating the reaction chamber to a negative pressure; (3) means for rapidly injecting a treatment gas into the reaction chamber, the treatment gas having an essentially predetermined composition comprising one or more components which are reactive with the at least one article within the reaction chamber; (4) means for removing the treatment gas from within the reaction chamber; and (5) means for replacing the treatment gas with an inert gas at about atmospheric pressure.